Apparatus for avoiding hot starts in turbojet engine operation and for igniting fuel in the afterburner



Nov. 17, 1953 W. o. THOMPSON 2,659,199

APPARATUS FoR AvoIoTNG HOT sTARTs IN TURBOJFT ENGINE OPERATION AND FoR IGNTTING FUEL IN THF AFTFRBURNER Filed sept. 9, 195o Patented Nov. 17, 1953 APPARATUS FOR AvoIDlNG HoT STARTS 1N TURBOJET ENGINE OPERATION AND Fon IGNITING FUELIN THE AFTERBURNER William O. Thompson, San Francisco, Calif. Application Yseptember 9, 195o, serial No. 184,002

1 Claim. j (Cl. 60-35.6)

The present invention relates to apparatus for avoiding hot starts in turbojet engine operation and for igniting fuel in an after burner thereof. In the operation of turbojet engines thereis a considerable delay in the ignitionpf the fuel charge with the result that the combustion chamber and the propulsion nozzle are all completely fllled with a combustible mixture before ignition occurs. When ignition occurs, it is frequently accompanied by a rather violent explosion and is evidenced by a tremendous burst of smoke and incompletely combusted material from the nozrle. This is very hazardous, both from the standpoint of t-he explosive force within the turbojet engine itself and because of fire hazards.

Another and somewhat related problem in the operation of turbojet engines, particularly those embodying an after burner, i. e., mechanism for introducing and burning additional fuel in the propulsion nozzle portion of the jet engine to the rear of the turbine, resides in insuring ready and immediate ignition of the auxiliary fuel supplied to the after burner.

It is among the purposes and objects of the present invention to provide apparatus for insurl ing immediate ignition of the primary fuel supply to the main combustion chamber ofthe turbojet engine, i. e. that combustion chamber positioned in advance of the turbine, and also for insuring immediate direct and positive ignition of auxiliary fuel when supplied to the after burner of the turbojet engine.

It has been heretofore propoeedto employ an after burner in association with a turbojet engine. However, great difficulty has been encountered in the practical application of this principle because of the great diculty in maintaining continuous ignition of the auxiliary supply of fuel admitted to the after burner. The velocity of theexhaust gases from the turbine including, of course, great quantities of excess air, is such that it tends to blow the flame completely out of the propulsion jet and preclude continuous combustion in the after burner. Obviously, if the after burner is to be effective, the fuel supplied thereto must be immediately consumed therein and this must take place despite the high velocity of the exhaust gases and excess air being delivered to the after burner from the turbine.

In its more specific aspects, the present invention contemplates the ignition of the fuel charge supplied either to the primary combustion chamber or to the after burnerof the turbojet or the simultaneous ignition of both the main fuel supply admitted to the primary combustion chamber and the auxiliary fuel supply admitted to the after burner by providing a pilot ame supported bya highly volatile, normally gaseous hydrocarbon in the form of propane or butane or mixtures thereof. The -pilot flame supported by such normally gaseous auxiliary hydrocarbon fuel is exceedingly effective in insuring immediate ignition of the main jet fuel suppliedv either to the primary combustion chamber of the turbojet engine or to the after burner thereof.

It is a further purpose and object ofthe inven` tion to introduce the pilot flame supporting fuel in vaporous condition'to either the primary cornbustion chamber or the after burner of the turbo` jet engine at a pressure at least equal to the pressure prevailing in such combustion zones of the turbojet engine.

More specific purposes and advantages of the invention will become apparent as the description proceeds, which will be given by reference to the accompanying drawing wherein Y.

Figure 1 is a diagrammatic view in side eleva-v tion illustrating one embodiment of an apparatus appropriate for practicing the invention.

Figure 2 is a fragmentary-diagrammatic view of an alternative embodiment conforming to the invention.

Referring to Figure 1, the power plant or turbojet engine is indicated generally at I0, with the intake end I I at the left of this figure. The power plant comprises anouter shell or casing structure I2 having an air duct I3 extending fore and aft with respect to the aircraft. The casing I2 has mounted therein along its longitudinal axis a nose portion I4 in which fuel lubricating oil pumps and appropriate igniting `apparatus may be housed. There is provided an axial flow multi-stage compressor I 5, a primary combustion apparatus I 6, a turbine I'I, an after burner I8 and a propulsion jet I9 dened by the casing I2, and a tail piece 20 mounted concentrically therein. Air enters at the intake end II, and flows back through the compressor I5 wherein it is compressed, and thence into the primary combustion apparatus I6, wherein it is heated. lThe heated compressed air, on leaving the combustion apparatus I6, is directed by appropriate guide vanes or nozzles 2I against the blades of the tur bine rotor I1, and thence passes around the after burner I8 to and through the propulsion jet I. The combustion apparatus I6 may be of any suit-v able construction, and is here shown as comprising a plurality of flared burner tubes 22 provided with openings 23 in the walls thereof through which the compressed air enters the tubes 22 and mixes with the jet fuel in the form of kerosene or other relatively high boiling fuel supplied to the burner tubes 22 by means of pipes 24 which lead to a source of jet fuel not shown. A suitable igniter in the form of a spark plug is mounted in the fuel receiving end of each of the burner tubes 22.

The excess airdischarged with the products of combustion through the turbine l1 is adequate to support combustion of additional jet fuel which is supplied to the after burner i8 through the line 25 which may lead to appropriate controls also associated with the fuel supply lines 24 for appropriately controlling thevsu'pply of jet fuel selectively to the primary combustion zone represented by the burner tubes 22 or tov the" after burner I8, or as is more frequently the case simultaneously to both the primary combustion zone' embracing tubes 22, and to the after burner i8. The after burner i8 is provided with openings 26 through which the excess air enters to be mixed with the auxiliary fuel supply entering through thelines 25. A suitable spark plug is mounted inthe fuel oil receiving end of the after burner I3,

As hereinbefore indicated, it is the purpose of the present invention to insure against hot starts in the operation of the turbejet engine andalso to provide for the continuous, uninterrupted combustion of auxiliary fuel in the after burner during those periods when the after burner is notbeing used. VFor these purposes, there is disclosed in the embodiment oi Figure l an annular header 21 from which a plurality of pilot fuel. supply conduits 28 extend to the burners 22. The pilot fuel conduits 28 preferably discharge the pilot fuel conveyed thereby into the chambers 22 closely adjacent to the associated igniter which preferably takes the` form of a suitable spark plug. The pilot fuel is supplied to the burners at a point spaced a short distance from the point of introduction' of the normal relatively high boiling jet fuel being supplied to the burners 22.

It will be observed that the annular header 21 is common to all of the burners 22.- The annular header 21 receives its supply of normally gaseous hydrocarbons, for example propane,froirl the auxiliary pilot fuel supply chamber 29 having a liquid ll 3U. The-liquified propane vor other lio'uifiable normally' gaseous hydrocarbon is mai-ntaied the' chamber 29 under the appropriate predetermined pressure, 'which at' all times will he maintained' greater than the operating: pres-i sure prevailingin the' burners" 22 of the tuihojet engine. Liqueed gaseous hydrocarbons' pass from the bottom of the chamber 23 through the line 3| to the vaporizei 32 supplied with any' suit-"- able source of hea-t to ele'c't requisite vaporisa-4 tion at the prevailing `messu're of the liduied gaseous hydrocarbong- Vapor's from the vaporizer 32 pass through line 33 and .re-enter the tank 23 to thereby maintain a constaht suppl-if' of! high pressure vaporou's, gaseous hydrocarbori's directly available for delivery to the primary combustion done represented by the burners 22 ofvthefturboj't engine.

Before describing the details by which high pressure vaporous, 'normally gaseous hydrocar= bons are supplied from the tank 29 to the burners 22 to initiate and support a pilot ilar'ne therein, it is desired to refer briefly to the provisionoi means for also supplying vaporous, normally gaseous hydrocarbons to theafter burner lato' initiate and support a pilot name therein to iii-A sure continuous combustion of fuel 'pe riods when it is supplied to the after burner I8 through the line 25. Line 34 leading from header 35 is adapted to convey high pressure vaporous hydrocarbons into the after burner I8 at a point adjacent a spark plug igniter for initiating and supporting a pilot flame in the after burner i8. A second branch line 35 extends from the header 35 for conveying high pressure vaporous hydrocarbons to the annular header 21 to be supplied therefrom by branch lines 28 to the burners 22. rIfhe header 35 upstream of the branch lines 34 and 36. is provided with a master solenoid valve itY downstream'- f'roih" the pressure regulator 38. The circuit for the master solenoid valve 31 is, of course, under control of the turbine engine operator, usually the pilot of the jet propelled aircraft, and whenV the master valve 31 is closed, there is no supply of high pressure vaporous hydrocarbons to either the primary combustion zone of the turbine engine embracing the burners 22, or to the after burner I8. A further solenoid valve 39 is disposed in the branch line 3G leading from the header 35 to the annular header 21 in the primary combustion chamber, and there is still a further solenoid valve l0 disposed in the branch line 3s leading from the header 35 to the after burner I8. The solenoid valves 39 and 4c are in a common circuit controlled by the toggle switch 4l. The solenoid valves 39 and 49 are normally biased to open position, so that Whenthe toggle switch is open or in the position shown in Figure 1, valves 39 and 40 are operi.` Uni der these conditions, actuation of the'master soles noid valve 31 which is normally biased to closed position will eiect an open communication from the storage tank 29' through header 35 and branch lines 3c andr 36 'for the simultaneous combustion of high pressureA vaporous hydrocarbone to both the annular header 2'1 in the primary combustion chamber of the turbo'jet engine and to the after burner i8 to thereby initiate and support a pilot llame in each of these zones effective to immediately ignite and mairie tain continuous combustion of jet fuel supplied thereto. There will be occasions in the operai tion of the turbojet engine when it is' desirable to initiate and support a pilot .dame in both the primary combustion chamber and the after turna er'. This is particularly true during take-oit' of the iet propelled plane, and sometimes occasions during flight thereof; Quite frequently, however, it will be desirable to initiate and sup port a pilot llame in the primary combustion chamber of the turbojetengine represented in the exemplied embodiment betweenvburners 22' during a period when the after burner i8 is not' i'n use. To effect this result, it is only necessary to move the toggle switch 4l into contact with terminal 42 to close a circuit through the solenoia and close that valve which will then pie; clude thev passage of high pressure vaporous hydrocarbons to the after burner 18. Alter natively, there may be occasions when it is dsii-ed to initiate and support a pilot flame in the after burner la', when no pilot flame is required in the primary combustion cham-ber of theturbo jet engine. To accomplish this result, it' is only necessary to move the toggleswitch 4| into contact with the terminal 43 to thereby effect actuation of the solenoid valve 39 to close the same, aiid thuscut olf possibility of supply high pressure vaporous hydrocarbon via branch line 36 to the' annular header 21.

It will thus be observed that in the embodi= ments of Figure l of the invention high pressure vaporous hydrocarbons, preferably propane, may be continuously supplied to support a pilot ame in both the primary combustion chamber and the burner of the turbojet engine. Likewise, the supply to both of these zones may be intermittent and instantaneous. Additionally, the high pressure vaporous hydrocarbon may be selectively supplied to either the primary combustion zone or to the after burner of the turbojet engine. When starting the turbojet engine, it will be commonly found desirable to close the solenoid vailve 40 and to open the solenoid Valve 31. In this way, a pilot iiame will be initiated and maintained in the primary combustion zone to insure the instantaneous ignition of the jet fuel supplied thereto, and to avoid commonly termed hot starts which flow from delayed ignition in the initial starting of the. engine.

In Figure 2 an alternative embodiment which provides for controlled intermittent supply of high pressure gaseous hydrocarbon to the primary combustion zone, and the after burner of the turbojet engine is disclosed. In this embodiment, a bank of any desired number of precharged cartridges 44 lcontaining liquied gaseous hydrocarbon such as propane, are p-rovided. The cartridges 44 are replaceable, so `that when one or more of them have been emptied, they may be removed from the permanent parts of the installation, and charged cartridges substituted therefor. To facilitate this replacement, an appropriate screw-type connection 45 is provided for each cartridge 44. It will be understood that the arrangement is such that when a charged cartridge 44 is placed in the system, it will be vented into the system through the action of the screw-type connection collar 45. From each chamber 44 an individual conduit 46 connects to a common header 41. In each conduit 46 there is disposed a suitable solenoid valve 48, each of which is disposed in la circuit individual thereto. The battery supply 49 operates the electrical source for these parallel circuits, which are individually closeable through the medium of switches 50 which may take the form of holdtype push buttons mounted on ya panel. The arrangement is such that when any given switch 50 is closed, the push button thereof remains in depressed position, indicating that the cartridge 44 associated with that particular push button, has been discharged.

The header 41 leads to a pressure regulator 5i comparable to the pressure regulator 38 in Figure 1, and it acts to reduce the pressure on the high pressure vaporous hydrocarbons from that pressure maintained in the header 41 to a constant lower pressure equal to or exceeding the pressure prevailing in the primary combustion chamber and the after burner of the turbojet engine. The header 41, when employing the alternating embodiment of Figure 2, may be substituted for the header 35 in Figure 1. In other Words, when the alternating embodiment of Figure 2 is being employed, the branch lines 34 yand CII 36 of the embodiment of Figure 1 Will be connected into the header 41 of Figure 2 on the downstream side of the pressure regulator 5|.

Vaporous hydrocarbons are maintained un-der the requisite predetermined high pressure in the respective cartridges 44 through the controlled supply of heat to the individual cartridges. To this end, the outlet of each cartridge 44 on the upstream side of the associate-d solenoid valve 48 leads through a line 52 to a pressure actuated electrical switch 53. The switch 53, associated with any given cartridge 44, is adapted to automatically close when the pressure in that cartridge falls below the predetermined minimum. The closing of any given switch 53 will establish the flow of current through the associated heater coil 54 with resulting limited vapor-ization of liquied gaseous hydrocarbons in that particular cartridge. When the required predetermined pressure has been restored in the cartridge, the associated switch 53 will open. The source of current for the heater coils 54 in this embodiment is the battery 55.

The embodiment of Figure 2 has certain advantages, particularly in aircraft operation, in that each cartridge carries a predetermined quan tity of liquied gaseous hydrocarbon, and can be readily replaced when discharged. The replacing of completely charged cartridges for discharged cartridges avoids the necessity for high pressure charging of large supply tanks carried on the aircraft. The foregoing description has been given by way of exemplication, and not in limitation thereof.

What I claim is:

An apparatus comprising a turbojet engine mounted in an aircraft, a primary combustion chamber in said engine, an afterburner in said engine, means for supplying normally liquid fuel to each of said primary combustion chamber and said afterburner, a pressure vessel for containing' a normally gaseous hydrocarbon in liquid form, selective means for supplying a normally gaseous hydrocarbon in vapor form from said pressure vessel to either of said primary combustion chamber and said aiterburner, and means for igniting and maintaining independent combustion of said normally gaseous hydrocarbon in either of said primary and secondary combustion chambers.

WILLIAM O. THOMPSON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,625,630 Scott Apr. 19, 1927 2,418,566 Arnhym Apr. 8, 1947 2,474,685 McCollum June 28, 1949 2,506,611 Neal et al May 9, 1950 2,520,434 Robson Aug. 29, 1950 2,540,642 Allen et al. Feb. 6, 1951 2,542,953 Williams Feb. 20, 1951 FOREIGN PATENTS Number Country Date 920,910 France Jan. 8, 1947 

